Luke already legitimately beat Rotj Vader, so he wins with far less difficulty.

__________________"Vader's pulse and breathing were machine-regulated, so they could not quicken; but something in his chest became more electric around his meetings with the Emperor; he could not say how. A feeling of fullness, of power, of dark and demon mastery -- of secret lusts, unrestrained passion, wild submission -- all these things were in Vader's heart as he neared his Emperor. These things and more."

nah, Vader would kill Luke without a thought if he wasn't his kid. This is outright told to us in ROTJ fight. Luke is not a full fledged Jedi even by the time of his fight with Vader on the Death Star and now with all this supplementary material like Rebels and the Vader comics we know this dude can clean house like nobodys business.

The official novelization of Return of the Jedi is canon in both Legends and the Disney Canon, and the novel tells us Vader was at his peak, and that he was bringing his full force to bear against Luke. If either of the two was holding back during the duel, it was Luke "I will not fight you" Skywalker, not Darth "You are unwise to lower your defenses!" Vader. Luke was overwhelming Vader at the start of that duel, in the movie, comic, and novel. The official comic adaption even tells us that Luke in RotJ has surpassed Vader.

That's not even getting into quotes from the movies, and the implied meanings. Sidious is eager to trade Vader for Luke, instructing Luke to kill Vader. Would he be so quick to dispose of his most powerful asset if this new apprentice weren't already more powerful than the last? Neither Yoda nor Ben doubt Luke's ability to defeat Vader when discussing Luke's destiny, repeatedly telling him that he is ready to face Vader. Meanwhile, in Empire Strikes Back, they were trying to warn him away from confronting Vader. Why the change of stance? Because Luke had grown powerful enough to defeat his father. Vader also comments on Luke's power in Return of the Jedi. "Your skills are complete. Indeed you are powerful, as the Emperor has foreseen." And how powerful did the Emperor foresee Luke being? "He could destroy us. The Force is strong with him. The son of Skywalker must not become a Jedi." Sidious feared that Luke could become strong enough to defeat both himself and Vader. Obi-Wan and Yoda seemed to have faith that RotJ Luke could defeat Vader and his master. Vader admitted in RotJ that Luke was as powerful as the Emperor had foreseen. Even the novel of Return of the Jedi shows that Sidious fears how powerful Luke has become.

In Legends, specifically Shadows of the Empire, Vader muses on his duel with Luke in Cloud City. While contemplating that duel, Vader admits that he had been actively trying to defeat Luke that whole time. In other words, Vader hadn't been holding back. Because if it had been easy to defeat Luke, then it was pointless to recruit him. And with that in mind, Vader finds himself believing that Luke, by the time of Empire Strikes Back, might be as powerful as Anakin Skywalker had been. After all, Luke very nearly defeated Vader on Bespin (scoring a hit on Vader's shoulder. An inch higher and he would have taken off Vader's head). Vader himself admits that if he hadn't confused Luke when he did (likely refering to the items he battered Luke with using telekinesis), Luke might have actually destroyed him then and there.

So, we have statements from various characters in the movies implying that Luke has greatly surpassed Vader, and is powerful enough to challenge the Emperor, from the Emperor himself, Vader himself, a man who has faced Vader and knows how powerful he is, and a Jedi Master who has faced the Emperor and knows how powerful he is. We have supporting evidence from the novel, which is still considered canon even after the great Legends purge, and the official comic (which I'm unsure whether or not is still considered canon, since a re-colored version of all three Marvel movie adaptations was recently released as 'official movie adaptations') both stating that Vader was going all-out in RotJ and that Luke was holding back, and still superior to Vader even then. And we have Legends speculation on Vader's part that Luke was actually more powerful than Anakin, and that in ESB, Vader only won due to superior skill in the Force breaking Luke's focus. With all that in mind, I feel I can handily give RotJ Luke the victory over ANH Vader, a version of the Sith Lord that is by all means inferior to the one that Luke had surpassed in RotJ.